Underbody Warming Systems with Core Temperature Monitoring

ABSTRACT

Apparatus and methods related to a non-invasive core temperature monitor for monitoring the temperature of a patient. In certain embodiments, the monitor may include a heated underbody support for heating at least a portion of a patient. The heated underbody support may include a low thermal mass heater and a temperature sensor. The heater may heat the peripheral thermal compartment of the patient to a temperature that is greater than the core temperature of the patient. The monitor may reduce the temperature of the low thermal mass heater to a set-point temperature that is less than the core temperature, allowing the temperature of the low thermal mass heater to move towards being in thermal equilibrium with the core body temperature. The core temperature may be determined when the peripheral thermal compartment of the patient is in substantial thermal equilibrium with the temperature of the core thermal compartment of the patient.

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication 61/977,930, filed Apr. 10, 2014, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

Some underbody support mattresses for use during medical procedures useinflatable chambers as the support mechanism. The patient must beallowed to “sink” into the inflatable chambers if they are going toprovide maximal surface contact with the patient's body in order tominimize the contact pressure at any given point, thus preventingpressure injury to the patient's skin. “Maximally” sinking into theinflatable chamber could be achieved by releasing air from the chamberuntil the moment before the most protruding body part of the patienttouches the base layer of the mattress or the hard surface below themattress. At this moment, the patient is maximally engulfed andsupported by the mattress, much like floating in water. The problem isthat there is currently no reliable way of determining when the mostprotruding patient part is near bottoming out versus actually touchingthe bottom.

Currently available underbody support mattresses with inflatablechambers adjust to a desired air pressure that is determined by theoperator. Whether or not the patient sinks into the mattress and whetheror not the body part that is most protruding “bottoms out” by touchingthe base layer of the mattress is totally a function of the operatorguessing at the correct pressure setting. Some mattresses withinflatable chambers claim to analyze derivatives of the change inpressure to determine the optimal support pressure. However, none ofthese pressure-based control systems reliably allow the patient to sinkmaximally into the mattress until the most protruding body part is anoptimal 0.5-1.0 inches from bottoming out. In this condition, all bodyparts are supported by air and yet the mattress maximally accommodatesthe patient's body for maximal contact pressure relief—similar tofloating in water. There is a need for a better and more reliablecontrol mechanism for reliably determining the maximum safeaccommodation before any body part “bottoms out.” Additionally, there isa need for a safety sensor that can detect changes in body positioningand/or loss of air from the inflatable chambers resulting in inadvertent“bottoming out,” that may convert a safe condition into a dangerouscondition over time, for example due to an air leak.

In addition, there are challenges to accurately measuring core bodytemperature through the skin and peripheral thermal compartment. Thereis a need for accurately and non-invasively measuring core bodytemperature during medical procedures such as surgery.

Grounding electrodes have been used during surgery for many decades. Theelectrical pathway for the radio-frequency (RF) electro-surgical unitscan be completed by directly applying a grounding pad to the patient'sskin for direct electrical conduction. Alternately, grounding can beaccomplished by placing a larger electrode under the patient which isnot in direct electrical contact but rather creates a condition ofcapacitive coupling for grounding the RF electrical current, asdescribed; for example, in U.S. Pat. Nos. 6,053,910 and 6,214,000.However, these capacitive coupling electrodes have been generallyutilized as mattress overlays which are inconvenient, require extracleaning and are usually embedded into a heavy, cumbersome gel pad.

Keeping the patient from sliding off of the surgical table when thetable is tilted into a steep, head-down (Trendelenburg) position, is aconstant challenge for surgical personnel and a danger for the patient.This problem has gotten worse in recent years with the advent oflaparoscopic surgery and particularly with the advent of roboticsurgery. In both of these instances, the patients are regularly placedinto steep Trendelenburg so that gravity can move the internal organsout of the way of the laparoscopes. A reliable and convenient way ofstabilizing the patient on the surgical table is needed for theTrendelenburg and other unusual positions.

SUMMARY

The underbody support mattresses of this disclosure are intended for usein medical settings generally. These include the operating room, theemergency room, the intensive care unit, hospital rooms, nursing homesand other medical treatment locations. They may also be used in othersettings. Embodiments described in this application are related to U.S.Pub. Numbers 2012/0279953, 2012/0238901, and provisional applicationNos. 61/812,987 and 61/936,508, the disclosures of all of which areincorporated herein by reference.

Various embodiments include flexible and conformable heated underbodysupports including mattresses, mattress overlays, and pads for providingtherapeutic warming to a person, such as to a patient in an operatingroom setting. In various embodiments, the heated underbody support ismaximally flexible and conformable allowing the heated surface to deformand accommodate the person without reducing the accommodation ability ofany under-lying mattress, for example.

In some embodiments, the heated underbody support includes a heaterassembly and a layer of compressible material. The heater assembly mayinclude a heating element including a sheet of conductive fabric havinga top surface, a bottom surface, a first edge and an opposing secondedge, a length, and a width. The conductive fabric may include threadsseparately and individually coated with an electrically conductive orsemi-conductive material, with the coated threads of the fabric beingable to slide relative to each other such that the sheet is flexible andstretchable. The heater assembly may also include a first bus barextending along the entire first edge of the heating element and adaptedto receive a supply of electrical power, a second bus bar extendingalong the entire second edge of the heating element, and a temperaturesensor. The layer of compressible material may be adapted to conform toa person's body under pressure from a person resting upon the supportand to return to an original shape when pressure is removed. It may belocated beneath the heater assembly and may have a top surface and anopposing bottom surface, a length, and a width, with the length andwidth of the layer being approximately the same as the length and widthof the heater assembly.

In some embodiments, the bus bars may preferably be braided wire. Insome embodiments, it may be preferably to coat the bus bars with aflexible rubber material such as silicone rubber, during construction ofthe heater. While braided wire is relatively tolerant of repeatedflexion, if the flexion occurs enough times at the same spot, evenbraided wire bus bars can fracture and fail. Coating the bus bars withsilicone rubber can significantly increase the durability of the busbars to survive repeated flexion.

In some embodiments, the conductive or semi-conductive material ispolypyrrole. In some embodiments the compressible material includes afoam material and in some embodiments it includes one or more air filledchambers. In some embodiments, the heated underbody support alsoincludes a water resistant shell encasing the heater assembly, includingan upper shell and a lower shell that are sealed together along theiredges to form a bonded edge, with the heater assembly attached to theshell only along one or more edges of the heater assembly. In someembodiments, the heating element has a generally planar shape when notunder pressure. The heating element is adapted to stretch into a 3dimensional compound curve without wrinkling or folding whilemaintaining electrical conductivity in response to pressure, and mayreturn to the same generally planar shape when pressure is removed.

In some embodiments, the heated underbody support includes a heaterassembly including a flexible heating element comprising a sheet ofconductive fabric having a top surface, a bottom surface, a first edgeand an opposing second edge, a length, and a width, a first bus barextending along the first edge of the heating element and adapted toreceive a supply of electrical power, a second bus bar extending alongthe second edge of the heating element, and a temperature sensor. Theunderbody support may further include a layer of compressible supportmaterial located beneath the heater assembly, which conforms to apatient's body under pressure and returns to an original shape whenpressure is removed.

In some such embodiments, the heating element includes a fabric coatedwith a conductive or semi-conductive material, which may be a carbon ormetal containing polymer or ink, or may be a polymer such aspolypyrrole. In some embodiments, the heated underbody support alsoincludes a shell including two sheets of flexible shell materialsurrounding the heater assembly, the shell being a water resistantplastic film or fiber reinforced plastic film with the two sheets sealedtogether near the edges of the heater assembly. In some embodiments, theheated underbody support also includes a power supply and controller forregulating the supply of power to the first bus bar.

In some embodiments, the compressible material comprises one or moreflexible air filled chambers. In some such embodiments, the compressiblematerial is a foam material. The heater assembly may be attached to thetop surface of the layer of compressible material. In some embodiments,the heated underbody support includes a water resistant shell encasingthe heater assembly and having an upper shell and a lower shell that aresealed together along their edges to form a bonded edge. In some suchembodiments, one or more edges of the heater assembly may be sealed intothe bonded edge. In some embodiments, the heater assembly is attached tothe upper layer of water resistant shell material. In some embodiments,the heater assembly is attached to the shell only along one or moreedges of the heater assembly. In some embodiments, the heated underbodysupport also includes an electrical inlet, wherein the inlet is bondedto the upper shell and the lower shell and passes between them at thebonded edge.

In some embodiments, the heating element has a first Watt density whenin a generally planar shape and a second Watt density when stretchedinto a 3 dimensional shape such as a compound curve, with the first Wattdensity being greater than the second Watt density.

In some embodiments, the temperature sensor is adapted to monitor atemperature of the heating element and is located in contact with theheating element in a substantially central location upon which a patientwould be placed during normal use of the support. In some embodiments,the heated underbody support also includes a power supply and acontroller for regulating a supply of power to the first bus bar.

In some embodiments, the heated underbody support is a heated mattressand includes a heater assembly and a layer of compressible materialwhich conforms to a patient's body under pressure and returns to anoriginal shape when pressure is removed located beneath the heaterassembly. The layer of compressible material may include one or moreinflatable chambers positioned under the heater assembly. A flexible,water resistant cover may encase the heater assembly, the layer ofcompressible material and the inflatable chambers.

In some embodiments, the heated underbody support may also include oneor more additional inflatable chambers positioned under the layer ofcompressible material, with each of the inflatable chambers beingelongated, having a longitudinal axis and optionally being positionedside-by-side one another with their longitudinal axes extendingsubstantially from the first end to the second end of the support. Insome embodiments, the inflatable chambers can be inflated and deflatedin two groups while the support is in use, with the inflatable chambersbeing in alternating groups such that each inflatable chamber is in adifferent group from each inflatable chamber which is beside it.

In some embodiments, the heated underbody support includes a pluralityof additional inflatable chambers. In some embodiments, the inflatablechambers can each be inflated and deflated independently while thesupport is in use. In some embodiments, the inflatable chambers can allbe inflated and deflated simultaneously as a group while the support isin use. In some embodiments, the inflatable chambers can be inflated anddeflated in two or more groups while the support is in use. In someembodiments, each of the chambers belongs to one of two or more groups,and the support includes separate conduits to each group with eachconduit providing independent fluid communication to one of the groupsof inflatable chambers for independently introducing or removing airfrom that group of inflatable chambers.

In some embodiments, the heated underbody support also includes apressure sensor for measuring an actual internal air pressure of thegroups of inflatable chambers, and a controller including a comparatorfor comparing a desired internal air pressure for each group ofinflatable chambers with the actual internal air pressure of each groupof inflatable chambers. The controller may be operatively connected toeach of the conduits and to an air pump and may further include or beoperatively associated with a pressure adjusting assembly for adjustingthe actual internal pressure. The controller may be adapted to causeinflation or deflation of each group of inflatable chambers to adjustthe actual internal air pressure of each of the group of inflatablechambers toward the desired internal air pressure.

In some embodiments, each inflatable chamber within each group ofinflatable chambers is in fluid connection with every other inflatablechamber of its own group so that air pressure changes in one inflatablechamber redistribute to all of the other inflatable chambers in the samegroup. In some embodiments, an interface pressure is maintained on a topsurface of each group of chambers at a location which supports apatient's body during normal use, the interface pressure being below acapillary occlusion pressure threshold of 32 mm Hg.

In some embodiments, an inflation characteristic, such as the volume ofair within the inflatable chambers is controlled. Controlling the volumeof air is different than other air mattresses that control the pressurewithin the inflatable chambers. It is impossible to detect changes inpressure as the patient begins to “bottom out” and therefore pressurecontrol cannot reliably produce a state of “maximal accommodation” intothe mattress.

In some embodiments the underbody support includes flexible, optionallyradiolucent compression sensitive switches (e.g., compression sensingswitches) within one or more of the inflatable chambers. These switchesmay be sized to detect when the patient has sunk into a partiallyinflated mattress to a point of “maximal accommodation.” The switchesmay have a large surface area and may extend substantially the entirelength of the inflatable chamber. These compression sensitive switchesare positioned to detect a body part that is protruding down into thesupport mattress the furthest and to prevent that body part from“bottoming out” or touching the hard surface below the underbodysupport. The height of the inflatable chamber(s) at this point may bedetermined by the volume of the air in the chamber, not the pressure ofthe air in the chamber.

In some embodiments, the controller including a controller algorithm ofthe inflatable underbody support initiates the release of air from theinflated chambers after the patient is positioned on the support. Therelease of air allows the patient to sink into the support for maximalsurface contact and therefore minimal surface contact pressure. Maximalsurface contact occurs just before the most protruding body part“bottoms out” on the hard surface below. To achieve this, the air may bereleased from the inflatable chambers and the patient may be allowed tosink into the support until the most protruding body part reaches apredetermined distance from the bottom. At that point the mostprotruding body part may contact and close one or more of the switches.

In some embodiments the switch may be a compression switch, including aflexible compression sensitive switch. The switch may be radiolucent soas not to interfere with x-rays or other imaging systems. The closedswitch may allow a small electric current to flow to the controllerwhich may respond by stopping the air release and initiating the nextsequence in the controller algorithm. In some embodiments, thecontroller algorithm then energizes the air pumps to re-inflate theinflatable chambers until the most protruding body part no longercompresses the compression sensitive switch(es) and the electric currentno longer flows through the switch. In this position, the mostprotruding body part is accurately positioned at a predetermineddistance above the hard base surface. With the compression sensitiveswitch(es) in the open position, it can then function as a safetysensor, detecting shifts in patient positioning or loss of air from theinflatable chambers that may result in inadvertent “bottoming out.”Should the compression sensitive switch(es) close at this point, thecontroller algorithm may automatically add more air to the inflatablechambers until the switch(es) opens and/or may activate an alarm.

In some embodiments, the assembly of volume-controlled inflatablechambers is encased in a foam box-like structure. The box-like structureoperating in conjunction with the inflatable chambers, creates astructure that allows the side walls to hinge inward for strain reliefof the materials of the upper surface, in order to prevent “hammocking.”

In some embodiments, one or more temperature sensors are interposedbetween the heated underbody support and the back or dependent bodysurface of the patient. The heated underbody support warms theperipheral thermal compartment of the patient that is in contact withthe heated support surface of the underbody support, creating acondition of near thermal equilibrium between the core thermalcompartment and the peripheral thermal compartment of the patient'sback. In this situation, the skin temperature of the patient's back incontact with the heater accurately correlates with core bodytemperature.

In some embodiments, the underbody support includes a groundingelectrode for electro-surgical equipment, such as capacitive couplinggrounding electrodes as known in the art. This electrode may consist ofa sheet of flexible and preferably stretchable conductive fabric thatextends substantially across the entire surface area of the supportmattress. Some electrodes have been supplied as mattress overlays andare generally incorporated into one or more layers of gel pads which canresult in an overlay that is heavy, cumbersome and interferes withoptimal pressure off-loading. To avoid these problems, variousembodiments incorporate the electrode into the stack construction of theunderbody support, eliminating the need for a heavy and cumbersome gelpad.

In some embodiments, the underbody support or the related heatedelectric blankets incorporate certain materials that can protect thepolypyrrole heater (e.g., heating element 10), and other oxidizableelectrical components not just from liquids, but also from oxidizingagents such as hydrogen peroxide (H₂O₂) disinfecting solutions. In someembodiments, urethane film may be used as the shell material for theunderbody support or related blankets; however, urethane film isrelatively permeable to hydrogen peroxide vapors, allowing the highlyoxidizing vapors to enter the support or blanket. Once inside, theperoxide vapors may attack any oxidizable material. These vapors cancause oxidation and failure of electrical components, especiallypolypyrrole. In some embodiments, sacrificial materials are added thatcan be preferentially oxidized. Sacrificial materials are preferablyorganic materials such as cellulose. In some embodiments, materials thatare known to be catalysts for the breakdown reaction of peroxide towater and oxygen may be added. For example, manganese dioxide (MnO₂)powder or other sacrificial material may be added to one or more of thefabric or foam layers or adhered to the heater with adhesive.

In some embodiments, the underbody support uses the fact that thepatient sinks into the support and achieves maximal body surface contactwith the support, to aid in preventing the patient from sliding off ofthe surgical table when placed in the steep Trendelenburg position (headdown). In some embodiments, a sheet of fabric or other material that hasbeen at least partially coated on both sides with high-friction plasticor rubber may be interposed between the patient and the support in orderto increase the coefficient of friction. An example of this may be a PVCfoam or silicone rubber applied as a pattern of three dimensional raiseddots onto a fabric. In some embodiments, a foam cushion may be anchoredto the head end portion 410 of the support and extend onto the mattressportion at the head end portion 410 of the surgical table 412 for addedsafety.

In some embodiments, the underbody support includes a layer ofwater-circulating channels over the surface area of the underbodysupport. Cold water can be circulated through these channels forinducing therapeutic hypothermia or therapeutic cooling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a heater assembly in accordance withillustrative embodiments.

FIGS. 2. is a cross-sectional view of an underbody support in accordancewith illustrative embodiments, including the heater assembly of FIG. 1.

FIGS. 3-4. are cross-sectional views of an underbody support withoptional heater assembly in accordance with illustrative embodiments.

FIG. 5 is a cross-sectional view of an underbody support with optionalheater assembly in accordance with illustrative embodiments.

FIGS. 6-7 are cross-sectional views of an inflatable chamber including asensing device in accordance with illustrative embodiments.

FIGS. 8-11 are cross-sectional views of an inflatable chamber inaccordance with illustrative embodiments and a protruding part of thepatient.

FIG. 12 is an illustrative plot of the volume of a most depressedinflatable chamber vs. time in accordance with illustrative embodiments.

FIG. 13 is an illustrative plot of air pressure in an inflatable chambervs. time in accordance with illustrative embodiments.

FIG. 14 is a cross-sectional view of a compressive sensing switch inaccordance with illustrative embodiments.

FIG. 15 is a top view of the compressive sensing switch of FIG. 14 inaccordance with illustrative embodiments.

FIG. 16 is a cross-sectional view of an inflatable chamber surrounded bya box-like structure in accordance with illustrative embodiments.

FIG. 17 is a top view of the inflatable chamber and portions of thebox-like structure of FIG. 16 in accordance with illustrativeembodiments.

FIG. 18 is a cross-sectional view of the embodiment of the inflatablechamber and box-like structure of FIG. 17 as deformed by the weight of apatient in accordance with illustrative embodiments.

FIG. 19 is a cross-sectional view of a heater assembly overlaying anunderbody support in accordance with illustrative embodiments.

FIG. 20 is a cross section view of a heater assembly folded up against apatient's front and back side by an underbody support in accordance withillustrative embodiments.

FIG. 21 is a temperature sensor interposed between a heated underbodysupport and a body surface of the patient in accordance withillustrative embodiments.

FIG. 22 is an illustrative plot of skin temperature vs. time as measuredby the temperature sensor of FIG. 21 in accordance with illustrativeembodiments.

FIG. 23. is a top view of patient anchoring support features inaccordance with illustrative embodiments.

FIG. 24. is a cross-sectional view of an embodiment the patientanchoring support features of FIG. 23 in accordance with illustrativeembodiments.

FIGS. 25-27. are cross-sectional views of a layer of water-circulatingchannels in accordance with illustrative embodiments.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description providespractical illustrations for implementing various exemplary embodiments.Examples of constructions, materials, dimensions, and manufacturingprocesses are provided for selected elements, and all other elementsemploy that which is known to those of skill in the field. Those skilledin the art will recognize that many of the examples provided havesuitable alternatives that can be utilized.

Embodiments include underbody supports such as heated underbodysupports, including heated mattresses, heated mattress overlays, andheated pads. The term underbody support may be considered to encompassany surface situated below and in contact with a user in a generallyrecumbent position, such as a patient who may be undergoing surgery,including heated mattresses, heated mattress overlays and heated pads.

Heated mattress overlay embodiments may be identical to heated padembodiments, with the only difference being whether or not they are usedon top of a mattress. Furthermore, the difference between heated padembodiments and heated mattress embodiments may be the amount of supportand accommodation they provide, and some pads may be insufficientlysupportive to be used alone like a mattress. As such, the variousaspects which are described herein apply to mattresses, mattress overlayand pad embodiments, even if only one type of support is shown in thespecific example.

While there is repeated reference to “heated underbody supports” in thisdisclosure, it must be noted that the heat feature is not a necessarycomponent of every embodiment. Non-heated underbody support embodimentsare also anticipated.

Various embodiments improve patient warming effectiveness by increasingaccommodation of the patient into the heated mattress, mattress overlay,or pad, in other words, by increasing the contact area between thepatient's skin and the heated surface of the mattress or mattressoverlay. The heating element, and the foam or inflatable chambers (e.g.,air bladders) of the mattress, which may also be included, are easilydeformable to allow the patient to sink into the mattress, mattressoverlay, or pad. This accommodation increases the area of the patient'sskin surface in contact with the heated mattress, mattress overlay, orpad and minimizes the pressure applied to the patient at any givenpoint. It also increases the surface contact area for heat transfer andmaximizes blood flow to the skin in contact with the heat for optimalheat transfer. The accommodation of the patient into the mattress,mattress overlay, or pad is not hindered by a stiff, non-conforming,non-stretching, hammocking heater. Additionally, in various embodiments,the heating element is at or near the top surface of the underbodysupport, in thermally conductive contact with the patient's skin, notlocated beneath thick layers of foam or fibrous insulation.

As shown in FIGS. 1-2, the combination of the thermal warmingeffectiveness and the skin pressure reduction effectiveness of a heatedunderbody support 3 (e.g., FIGS. 2, 19 and 23) can be optimized when aheating element 10 is overlaying a layer, such as a compressiblematerial layer 20, that can provide maximal accommodation 22 of apatient (e.g., FIG. 23) positioned on the underbody support 3 (e.g.,mattress).

In this condition, the heating element 10 is in contact with a maximalamount of the patient's skin surface 232 which maximizes heat transferand pressure reduction. Heated underbody supports 3 made with inflatablechambers 170 (FIG. 2) forming or included in the compressible materiallayer 20, or in addition to the compressible material layer 20, can alsoprovide excellent accommodation. Further, a heated underbody support 3with excellent accommodation properties having a heating element 10 asdescribed herein avoids degrading the accommodation properties of theunderbody support 3 when a heater assembly 1 is added or included.Therefore, the combination of the heater assembly 1 design with anaccommodating underbody support 3, made with one or more inflatablechambers 170, is advantageous and synergistic for the effectiveness ofboth technologies. However, all features described herein may be usedindependently, or in combination with one another. For example, theunderbody support 3 described herein may or may not be: heated, includegrounding, have hydrogen peroxide protection, patient securing features,water circulating channels, or any other features described herein.Likewise, the heater assembly 1 described herein may or may not include:an underbody support 3, include grounding, have hydrogen peroxideprotection, patient securing features, water circulating channels, orany other feature described herein. Illustrative examples are provided,and all possible combinations of the features herein are consideredembodiments of this disclosure.

As shown in FIG. 1, some embodiments of the heater assembly 1 include aheating element 10 coupled by a layer of adhesive 30 to the layer ofcompressible material 20. The heating element 10, the layer ofcompressible material 20 and the adhesive 30 may then be encapsulatedand sealed by upper and lower shells 42, 44. The seal may be a hermeticseal.

In some embodiments, as shown in FIG. 2, bus bars 62, 64 of the heatingelement 10 are optionally made of braided wire. While braided wire isrelatively tolerant of repeated flexion, if the flexion occurs enoughtimes at the same spot, even braided wire bus bars can fracture andfail. In some embodiments, the bus bars 62, 64 may be braided wire busbars 62, 64 and may be coated with a flexible rubber-like material suchas silicone. The coating may be applied during construction of theheater assembly 1.

Coating the bus bars 62, 64 with silicone can vastly increase thedurability of the bus bars 62, 64 to repeated flexion. The silicone orother coating can serve at least two functions, first, it forces theindividual wire strands to form a larger radius during flexion andsecond, it stabilizes the individual wire strands so that they do notabrade each other during flexion. Thicker coats of silicone rubber orother material on the bus bars 62, 64 may provide more protection fromflexion fractures than thin coats.

Our testing has shown that braided bus bars, like bus bars 62, 64, sewnin parallel on a heating element 10 made from a piece heater materialsuch as a non-woven heater fabric, can be repeatedly and bent or flexedat a specific point. During testing all of the bus bars were flexedalong a single crease in the heater fabric, through a 360° arc, gentlycreasing the bend and then flexing it in the other direction though a360° arc. This process was repeated until the bus bars failed at thebend. Uncoated and thinly coated bus bars began to fail at approximately350 flexions and totally failed by 450 flexions. Bus bars with a“medium” coating of silicone rubber (approximately 1/32 inches thick)failed between 1900 and 2100 flexions. Bus bars with a “thick” coatingof silicone rubber (approximately 1/16 inches thick) showed no signs offailure after 2500 flexions.

FIGS. 2, 3 and 4 show an embodiment of an underbody support 3 comprisingone or more inflatable chambers 170 (e.g., air chamber, fluid chamber),and a heater assembly 1 overlaying the one or more inflatable chambers170. In some embodiments, a single inflatable chamber 170, or aplurality of elongated inflatable chambers 170 are positioned under theheater assembly 1. The plurality of elongated inflatable chambers 170may be cylindrical in shape and may be oriented in parallel andpositioned side-by-side one another, with their long axes extendingsubstantially from one side of the underbody support 3 mattress to theother side. However, other inflatable chamber 170 shapes andorientations are anticipated. The inflatable chambers 170 may be roundor ovoid in cross section. They may or may not be physically secured toan adjacent inflatable chamber 170. Alternately, they could be securedto a base sheet or simply positioned and contained within a cover 160(e.g., mattress cover) without being secured. The inflatable chambers170 may be made of a fiber-reinforced plastic film or a plastic filmthat has been bonded, laminated or extruded onto a woven or non-wovenfabric reinforcing layer. Urethane may be used as the plastic film, butother plastic film materials are anticipated. Woven nylon may be used asthe reinforcing layer, but other fabric materials are anticipated. Theinflatable chambers 170 may also be used for pressure reduction alone,in an underbody support 3 without a heater assembly 1 or heating element10.

The inflatable chambers 170 can be sealed and static, or connectedtogether in fluid connection to allow redistribution of air between theinflatable chambers 170. In some embodiments, the inflatable chamber 170can be actively inflated and deflated while the underbody support 3 isin use. The inflatable chambers 170 may be inflated and deflated eachindependently, all simultaneously, or in separate groups, while theunderbody support 3 is in use. In some embodiments, the inflatablechambers 170 are each a part of two separate groups and may besegregated, for example, by every other inflatable chamber 170 (e.g.,alternating inflatable chambers 170) according to their relativeside-by-side positions. A conduit or conduits may be in separateindependent fluid communication with each inflatable chamber 170 of thegroup of inflatable chambers 170 for independently introducing orremoving air from that group of inflatable chambers 170.

Alternately, there may be only a single group of inflatable chambers 170or there may be more than two groups of inflatable chambers 170 whichcan be separately inflated or deflated. If multiple groups of inflatablechambers 170 are used, they may or may not be evenly or symmetricallyarranged. For example, inflatable chamber 170 groups may be separatedaccording to the amount of weight-bearing associated with that area.Inflatable chambers 170 in greater weight bearing areas, such as thetorso and hips, may be in a first group, while inflatable chambers 170in areas bearing less weight, such as those supporting the head andlegs, may be a separate group of inflatable chambers 170. In this way,the lighter portions of the patient's body may be supported byinflatable chambers 170 that are inflated to a lower air pressure thaninflatable chambers 170 that support more weight/heavier body portions.

Inflatable chambers 170 may be secured to the adjacent inflatablechamber 170 or to a base sheet or may be secured by the ends to anelement running along each side of the underbody support 3, and in someembodiments the inflatable chambers 170 and their connectors for fluidconnection may be individually detachable. In this instance, if a singleinflatable chamber 170 or connector fails or is damaged, it can bereplaced without requiring the replacement of the entire inflatableunderbody support 3.

The material forming the inflatable chamber 170, such as a plastic film,may be bondable with RF, ultrasound, heat, solvent, or other bondingtechniques. The film or film layer of the laminate may be folded back onitself and a single longitudinal and two end bonds that may cooperate toform an inflatable chamber 170. More complex inflatable chamber 170construction and bonding embodiments are anticipated.

The conduit fluid connection for air flow to and from and between theinflatable chambers 170 may be plastic tubing, for example. The inletinto the inflatable chamber 170 can be through one of the bonded seamsor may be through a surface of the inflatable chamber 170. To preventocclusion of the tubing at the inlet, the tubing may extend one or moreinches into the inflatable chamber 170. Other conduits are anticipated,such as a molded or inflatable plenum that may run the length of theunderbody support 3.

In some embodiments such as FIG. 2, a heater assembly 1 (a heaterassembly 1 encased within a water resistant shell 42, 44) is placed ontop of the inflatable chambers 170 so that the conductive fabric heatingelement 10 is at or near the top surface of the underbody support 3.Alternately such as shown in FIG. 5, a heater assembly 1 (without ashell 42, 44) could be placed on top of the inflatable chambers 170 sothat the heating element 10 is at or near the top surface of theunderbody support 3 mattress. The underbody support 3 may include aflexible, water resistant cover 160 that encases the heater assembly 1and the inflatable chambers 170. Alternately as shown in FIG. 5, heaterassembly 1 could be placed on top of a polymeric foam pad 150 such asviscoelastic or urethane foam. In some embodiments the inflatablechambers 170 may be used as an underbody support 3 mattress without aheater assembly 1.

In some embodiments, the water resistant cover 160 is a plastic filmlaminated or extruded onto a woven or knit fabric such as “Naugahyde.”This construction is soft and durable. Alternately, the cover 160 can bemade of plastic film, fiber-reinforced plastic film or a plastic filmlaminated or bonded to a woven, non-woven, or knit fabric. Covering 160made of plastic film laminated or extruded onto a woven or knit fabricmay include sealed seams such as RF, ultrasound or heat, if the plasticfilm side is inverted into the seams so that layers of plastic film arein opposition to each other. Alternately, the polymer coated fabric iswell-suited to a sewing process for creating the seams. Seams created bya sewing process may advantageously include an adhesive bond for sealingthe sewn seam against liquid intrusion.

The heater assembly 1 of the underbody support 3 may be “free floating”within the water resistant cover 160 of the underbody support 3.Alternately, the heater assembly 1 may be attached to the inflatablechamber 170 or foam pad 150, or attached to the cover 160, either at theedges of the heater assembly 1 or on or across the top or bottom surfaceof the heater assembly 1.

One or more edges of the heater assembly 1, such as two or four edges,may be attached to the ends of the elongated inflatable chambers 170 orcompressible material layer 20 by snaps, Velcro or any other suitableforms of attachment. Such embodiments may stabilize the heater assembly1 within the underbody support 3. A series of independent securing tabsor flaps may extend laterally from the bonds 48 of the heater assembly 1encapsulation shell 42, 44. As the inflatable chambers 170 inflate andbecome turgid, they simultaneously stretch the heater assembly 1laterally, assuring that the heating element 10 cannot wrinkle and foldon itself or become displaced.

In some embodiments, an inflation characteristic such as the volume ofair within the inflatable chambers 170 is controlled. Controlling thevolume of air is different than all other air mattresses known to theinstant inventors that control the pressure within the inflatablechambers 170. In other systems, it is impossible to detect changes inpressure as the patient begins to “bottom out” and therefore pressurecontrol cannot reliably produce a state of “maximal accommodation” intothe mattress. In contrast, controlling for and measuring an inflationcharacteristic (e.g., air volume, indication of near collapse, adistance between portions of the inflatable chamber 170) in the mostdepressed inflatable chamber 170 with an appropriate sensor, can insure“maximal accommodation.” “Maximal accommodation” is the point when thepatient has maximally sunk into the underbody support 3, but has not yettouched the hard base with their most protruding body part 230 (e.g.,FIGS. 8-11). A variety of sensing technologies for determining airvolume within the inflatable chambers 170 may be used in variousembodiments.

As in FIGS. 6 and 7, some embodiments of the underbody support 3 includesensing devices such as switches 200. Switches 200 may be flexible,radiolucent compression sensing devices within one or more of theinflatable chambers 170. In some embodiments, switches 200 may be othertypes of switches other than flexible, radiolucent compression sensitiveswitches. The switches 200 may be positioned to sense the patient bodypart that is protruding down into the underbody support 3 the furthestand to prevent that body part from “bottoming out” or touching the hardsurface below the underbody support 3. Since the “most protruding bodypart,” or portion of the body sinking deepest into the underbody support3 (e.g., element 230, FIGS. 8-11), is unpredictable (buttocks, hip,elbow, shoulder), the location of the most protruding body part on theunderbody support 3 is also unpredictable. Therefore, the switches 200are preferably located in each of the inflatable chambers 170 and have alarge surface area relative to the inflatable chamber 170 size.

In the embodiment of FIGS. 6 and 7, the compression sensitive switches200 are sized and shaped to fit the size and shape of the inflatablechamber 170 and to activate at a given volume of air that correlateswith the height thickness of the switch 200. In the case of a tubularinflatable chamber 170, the switches 200 are preferably relatively wide,covering 0.3-0.7 of the diameter of the inflated inflatable chamber 170(FIG. 6) and preferably extending substantially the entire length of theinflatable chamber 170 (FIG. 7). For example, if the inflatable chamber170 is 3 inches in diameter and is 18 inches long, the surface area ofthe switch 200 may be 1-2 inches wide and 16 inches long. Other switch200 widths and lengths are anticipated. The relatively large surfacearea of the individual switches 200, and the arrangement of theindividual switches 200 into a pattern may cover substantially thesurface area of the underbody support 3. This assures that the “mostprotruding body part” at any location on the surface of the underbodysupport 3 can be detected.

The compression sensitive switches 200 may be physically located withinthe inflatable chamber(s) 170, so that they are protected from randomcompression by the adjacent inflatable chamber 170, when the inflatablechamber 170 is inflated and the underbody support 3 is in use. In someembodiments, being located within the inflatable chamber 170 alsoprotects the switch 200 from damage. It also assures that thecompression sensitive switch 200 is contacted by “the most protrudingbody part” 230 (FIGS. 8-11) at a precise height above bottoming outagainst the hard base, or above the bottom of the inflatable chamber 170or other surface, which allows maximum accommodation of the patient 230(FIGS. 8-11) into the underbody support 3 and yet protects againstbottoming out. For example, in FIGS. 8 and 9, if the inflatable chamber170 has a cross-sectional diameter of 3 inches, the switch 200 maypreferably be designed to sense contact when “the most protruding part”of the patient 230 is 0.75-1.0 inches above bottoming out. This heightcorrelates with a given volume of air in the inflatable chamber 170.Other switch contact heights are anticipated which correlate with othervolumes of air. If additional accommodation of the patient into thesupport is desirable, the switch 200 may be designed to sense contact ata height of less than 0.75 inches. If added safety is desired, theswitch 200 may be designed to sense contact at a height of more than 1.0inches. While the compression sensitive switches 200 disclosed hereinmay be preferred, other types and construction of switches, includingvolume measuring switches and distance measuring switches areanticipated.

Other switches 200, such as pressure-sensing membrane switches arewell-known in the art. Pressure-sensing membrane switches generallyconsist of two separated metal foil contacts that can be pressedtogether to make contact in response to applied pressure. The precisepositioning of the metal foil is determined by the shape of the stiffplastic film (membrane) to which the foil is applied. These switches areminimally flexible because flexion may cause the metal foil contacts toclose in the absence of applied pressure. These membrane switches arehard, generally made of a stiff plastic film adhered to a hard surfacelike metal or glass in order to protect the fragile metal foil contacts.Finally, the metal foil conductors and contacts are radio-opaque,meaning that they show up on x-ray. While these pressure sensingmembrane switches may be used in various embodiments, the switches 200used in various embodiments may alternatively be flexible, radiolucent,durable compression sensitive switches, and not require mounting to ahard surface to assure proper functioning. The instant invention may useany other suitable type of switch.

As shown in FIGS. 6-9, the compression sensitive switches 200 of theinstant invention may use electrically conductive fabric pieces as theconductor and/or contacts 202, 204. The conductive fabric pieces (e.g.,202, 204) may be polypyrrole coated onto any woven or non-woven fabric.Alternately, the conductive fabric in the switch 200 may be carbon fiberfabric or fabric that has been coated with conductive ink or metal suchas silver. Alternately, the conductor 202, 204 in the switch 200 may beconductive ink applied to polymeric film or conductive materials such ascarbon or metal impregnated into polymeric films.

For the following description, it is assumed that the inflatedinflatable chamber 170 is a tube that is approximately 3 inches indiameter and 18 inches long as in FIGS. 6 and 7. However, the size andshape of the compression sensitive switches 200 may change forinflatable chambers 170 of other sizes and shapes. The contacts 202, 204and conductors of the switch 200 may include two pieces of conductivefabric. In this example, each of the two pieces of the conductive fabriccontacts 202, 204 may be 1.5 inches wide and 16 inches long. The twoconductive fabric contacts 202, 204 may be adhesively bonded to bothsides of a strip of compressible material that forms a compressibleswitch layer 206. The compressible switch layer 206 may be a resilientopen-cell foam material, such as urethane foam. However, other materialssuch as polymeric foam materials or high-loft fibrous materials may beused.

In some embodiments, the compressible switch layer 206 may be 3/16-¾inches thick, however, other thicknesses of compressible switch layers206 may be used. One or more holes 208 may be cut through thecompressible switch layer 206. Preferably, a pattern of multiple holes208 may be cut through the compressible switch layer 206. The size andshape of the holes 208 may be determined by the thickness, size, shapeand compressibility of the compressible switch layer 206. For example,if the compressible switch layer 206 is 3/16 inch thick, the holes 208may be ½-¾ inches in diameter. If the compressible switch layer 206 is ¾inches thick, the holes 208 may be ¾-1 inch in diameter. Embodimentsinclude holes 208 of various number, shape, size and pattern.

In the embodiment of FIGS. 6 and 7, the compression sensitive switches200 may also include two layers of compressible foam. An uppercompressible foam layer 210 and a lower compressible foam layer 212,sandwiching the conductive fabric pieces/contacts 202, 204 and thecompressible switch layer 206 there-between. The compressible foamlayers 210, 212 may be attached to the conductive fabric pieces/contacts202, 204 with adhesive forming a five-layer sandwich construction. Thecompressible foam layers 210, 212 may be ¼-½ inches thick but otherthicknesses may be used. Many foam materials are suitable including opencell urethane. While foam may be used for these layers, other materialssuch a high-loft fibrous materials may also be used. The lowercompressible foam layer 212 that is positioned on the bottom side of theswitch 200 may be tapered toward its long edges in order to seat in thecurved shape of the inflated inflatable chamber 170. Curving the lowercompressible foam layer 212 allows the conductive fabric pieces 202, 204and the compressible switch layer 206 (the active part of the switch) toremain relatively flat, despite being located within a curved chamber.

When the compressible switch layer 206 is compressed as shown in FIGS. 8and 9, the two pieces of conductive fabric 202, 204 contact each otherwithin the space(s) created by the one or more holes 208. A wireconductor may be attached to each of the conductive fabriccontacts/pieces 202, 204. A small electric potential is applied to theconductive fabric contacts/pieces 202, 204 and when they contact eachother, an electric current flows through the switch 200, activating thecontroller.

The controller may be activated by active feedback data derived from thecurrent flowing through one or more of the compressed compressionsensitive switches 200. This signal allows the system to maintain adesired internal air volume within the most depressed inflatable chamber170 by adjusting the amount of inflation of the most depressedinflatable chamber 170 or of the groups of inflatable chambers 170, suchas first and second groups of inflatable chambers 170. Controlling theair volume in the most depressed inflatable chamber 170 independent ofair pressure, allows maximal accommodation of the patient 230 into theinflatable underbody support 3. This is in contrast to all otherair-filled support mattresses and air-filled support surfaces known tothe instant inventors, which rely on controlling air pressure.

FIG. 12 illustrates the volume vs. time curve measured when air isreleased from the most depressed inflatable chamber 170 with a patientlaying on the underbody support 3 mattress. This allows the patient toprogressively sink into the underbody support 3, which if carried to aconclusion would result in the patient laying on the hard base layerwithout any air there between at point E. However, when the volumedecreases to the point B where the compression sensitive switch(es) 200is compressed in the most depressed inflatable chamber 170, deflation isreliably stopped before the patient “bottoms out,” point E. Thiscondition is also illustrated in FIGS. 8 and 9.

In contrast, FIG. 13 illustrates the pressure vs. time curve measuredwhen air is released from the inflatable chambers 170 with a patientlaying on the underbody support 3. This allows the patient toprogressively sink into the underbody support 3, which if carried to aconclusion would result in the patient laying on the hard base layerwithout any air there between. At time F, the chambers 170 are inflatedto a pressure that is higher than the pressure exerted by the weight ofthe patient. With deflation, the pressure gradually drops and at time Gthe pressure in the underbody support 3 is determined by the weight andgeometry of the patient. With continued deflation, the pressure remainssubstantially unchanged as the patient continues to sink into thedeflating underbody support (G

I). At time H, the most protruding point of the patient 230 (FIGS. 8-11)bottoms out on the hard base layer; however, no change in pressure isnoted despite “bottoming out” having occurred. A reduction in measuredpressure is not noted until time I, when a majority of the patient is“bottomed out” and is resting on the hard base layer of the underbodysupport 3.

From FIG. 12, it is apparent that the precise switch 200 closure at timeB as shown in FIGS. 8 and 9, indicating that the appropriate “maximalaccommodation” volume has been reached, is a safe and reliable way tooptimally support the patient. In contrast, the subtle changes inpressure shown in FIG. 13 cannot be reliably detected and do notcorrelate with the “bottoming out” (H) of the patient's most protrudingpart. Therefore, it should be evident that controlling the inflatablechambers 170 of this support surface by detecting and controlling airvolume is a significant improvement in reliability and safety comparedto the standard method of detecting and controlling air pressure.

Alternately, or additionally, the inflatable underbody support 3 mayinclude pressure sensor assemblies capable of detecting, in real time,the actual internal air pressure of the inflatable chambers 170 and mayalso include a comparator which may be in operational communication withthe controller for comparing a desired internal air pressure value ofthe inflatable chambers 170 with the actual internal air pressure, and apressure adjusting assembly, also in operational communication with thecontroller, for adjusting the actual internal pressure. The controllermay be activated by active feedback data derived from the comparator formaintaining a desired internal pressure value in the inflatable chambers170 by adjusting the amount of inflation of the inflatable chamber 170or of the groups of inflatable chambers 170, such as first and secondgroups of inflatable chambers 170.

The controller may be operationally connected to a first conduit and asecond (or multiple) conduit and a pump for inflating the inflatablechamber 170 or plurality of inflatable chambers 170. Each inflatablechamber or plurality of chambers 170 may be independent of each otherinflatable chamber 170 so that each inflatable chamber 170 may react toair pressure changes independently, or may be connected as a group andmay react in concert with the air pressure changes in the otherinflatable chambers 170 of the group. The air may be redistributedwithin the chambers 170 and the interface pressure may be maintained atany point on the top surface of each of the plurality of chambers 170which is engaged with an anatomical portion of the user's body, at anaverage pressure below a capillary occlusion pressure threshold of 32 mmHg, for example.

The total thickness of the compression sensitive switch 200 isdetermined by the desired distance between the patient's “mostprotruding part” 230 (FIGS. 8-11) and the point of “bottoming out.” Forexample, if the desired resting distance between the most protrudingpart and the base of the support is ¾-1 inch, the total thickness of thestack of materials forming the compression sensitive switch 200 shouldbe approximately 1-1¼ inch. This may consist of an upper compressiblefoam layer 210 that is ¼ inch thick and a compressible switch layer 206that is ¼ thick and a lower compressible foam layer 212 that is ½-¾ inchthick. Other heights and thicknesses are anticipated.

As shown in FIGS. 8-11, the entire switch 200 assembly may be alaminated compression sensitive switch 200 advantageously encapsulatedin a durable and preferably vapor resistant switch encapsulation shell214 for added durability and protection from mechanical and chemicaldamage. The encapsulation material may be a coating such as siliconerubber, urethane, PVC or neoprene. A spray-on vinyl coating may beapplied to the outer surface of switch 200. Alternately, the switchencapsulation shell 214 may be made of one or more layers of plasticfilm such as urethane or PVC, formed into a sealed shell,hermetically-sealed or otherwise. Other suitable polymeric encapsulationmaterials and techniques are anticipated.

As shown in FIGS. 6 and 7, the entire compression sensitive switch 200may be located within an inflatable chamber 170. The switch 200 may beanchored into a specific position, such as at the bottom of theinflatable chamber 170. However, in some embodiments, the switch couldbe attached to the top of the inflatable chamber 170. The switch 200 maybe bonded to the material of the inflatable chamber 170 with adhesive orby thermal bonding techniques. Alternately the switch encapsulationshell 214 may include one or more stripes of plastic film material thatcan be bonded to the inflatable chamber 170 material. For example,plastic film may extend from each end of the switch 200 and be bondedinto the bonded seam forming the ends of the inflatable chambers 170.

In some embodiments, the controller algorithm inflates the inflatableunderbody support 3 to a predetermined air pressure such as 1 psi, whilethe patient is being moved and positioned on the underbody support 3(FIG. 13, Time F). Positioning the patient is facilitated by having theunderbody support 3 in a relatively firm condition, preventing thepatient from sinking into the underbody support as shown in FIGS. 6 and7.

In some embodiments, the controller is then signaled, for example, bythe operator pressing an operation switch, that the patient ispositioned and the controller should initiate the algorithm thatreleases air from the inflated inflatable chambers 170. Alternately, thecontroller may automatically sense the positioning of the patient by achange in air pressure in the underbody support 3 caused by thepatient's weight and initiate the algorithm to start. The release of airmay allow the patient to sink into the underbody support 3 for maximalsurface contact with the patient's skin and therefore minimal surfacecontact pressure with the skin (FIG. 12, Time AB).

Maximal surface contact may occur just before the most protruding bodypart 230 (FIGS. 8-11) “bottoms out” on the hard surface below. In thisposition, the patient is as close to floating (as in floating in water)as can be achieved with an inflatable underbody support 3 of any giventhickness. The air may be released and the patient may be allowed tosink into the underbody support until the most protruding body part 230reaches a predetermined distance from the bottom of the most depressedinflatable chamber 170. At that point the most protruding body part 230contacts and closes one or more switches 200 (e.g., flexible,radiolucent compression sensitive switches) (FIG. 12, Time B). Thissituation is also illustrated in FIGS. 8 and 9.

The closed switch 200 allows a small electric current to flow to thecontroller activating the next step in the sequence of the algorithm,which stops the air release. In some embodiments, the next sequence inthe controller algorithm is then activated and it energizes the airpumps to re-inflate the inflatable chambers 170 until the mostprotruding body part of the patient 230 is lifted and no longercompresses the compression sensing or pressure sensing switch 200 withinthe most depressed inflatable chamber 170 and the electric current is nolonger flowing through the switch 200 (FIG. 12, point C). This situationis also illustrated in FIGS. 10 and 11. In this position, the mostprotruding body part of the patient 230 is accurately positioned at apredetermined distance above hard base surface. To achieve and maintainthis maximally accommodating position, the air volume within theinflatable chambers 170 must be controlled, not the air pressure.

With the compression sensitive switch 200 in the open position, it canthen function as a safety sensor, detecting shifts in patientpositioning or inadvertent loss of air from the inflatable chambers 170that may result in “bottoming out.” Should the switch 200 re-closeduring the operation (FIG. 12, point D), reestablishing the situationillustrated in FIGS. 8 and 9, the controller will sense the electricalcurrent flow and the algorithm may automatically activate the air pumpsto inflate the inflatable chambers 170 until the switch 200 once againopens and/or an alarm may be activated.

The safety sensor feature of the compression sensitive switch(es) canalso be used to document that the patient did not have a body part thatwas inadvertently “bottomed out” for a prolonged period during theoperation. This information can be automatically transmitted to theelectronic medical record (EMR) for documentation. Documentation thatthe patient did not “bottom out” during surgery indicates that thepatient was well supported and protects the surgical staff from blameshould a pressure ulcer later form.

At the end of the surgical or medical procedure, the operator may onceagain signal the controller, such as by pressing a switch, to initiatethe algorithm that energizes the air pumps to re-inflate the inflatablechambers 170 to a predetermined air pressure. The relatively firmunderbody support 3 may facilitate moving the patient off of theunderbody support 3.

Embodiments of the switches 200 for control of the volume of air withinthe inflatable chambers 170 have been disclosed. Other technologies fordetecting air volume or a minimum distance/clearance between portions ofthe inflatable chambers 170 may alternatively be used. Other designs ofswitches 200, such as compression sensitive switches including differentmaterials, different stacks of materials and different constructions mayalso be used. Different algorithms used to control the function of theinflatable chambers 170 in response to inputs from the volume sensors orcompression sensitive switches 200 may also be used in variousembodiments.

In some embodiments, the inflatable chambers 170 of the underbodysupport 3 include a surrounding structure that preferably may be made offoam. As shown in FIGS. 16-18, the compressible material layer 20 may bea layer of foam positioned on top of the inflatable chambers 170. Manytypes of foam are anticipated for this use but urethane upholstery foamthat is both durable and inexpensive may be used. Two flexible sidewalls 80, 82 may also be made of foam and may be bonded 84 (FIG. 18) tothe compressible material layer 20. Two flexible end walls 88, 90 mayalso be made of foam and may be bonded 84 to the compressible materiallayer 20 and bonded 98 (FIG. 18) to the flexible side walls 80, 82. Theresulting box-like structure 92 may be open on the bottom and fit overthe assembly of inflatable chambers 170, creating the externalappearance of a cut foam mattress, rather than the rounded and poorlyfitted look of the inflatable chambers 170. In some embodiments, thebonded joints 84 and 98 may be reinforced by bonding a layer of fabricto the foam adjacent the joints with the fabric traversing the jointsfor added strength.

In some embodiments, the box-like structure 92 may be made of foam andmay sit on a base layer 86, also optionally made of foam. The fasteners94 between the flexible side 80, 82 (FIG. 16), the end walls 88, 90(FIG. 17), and the base layer 86 are preferably detachable. Thefasteners 94 may be strips of Velcro hook and loop fasteners. However,other fasteners such as zippers and snaps may be used. The box-likestructure 92 may be encased within a water resistant cover 160.

The box-like structure 92 of this invention may not only improve thecosmetic appearance of the underbody support 3 compared to the look oftubular inflatable chambers 170, it may also serve the function ofpreventing “hammocking.” Hammocking occurs when the materials of theupper surface of a support or mattress cannot stretch adequately toallow the patient to optimally sink into the support. If the materialsof the upper surface of the support are stretched laterally, thematerials may act like a cot or hammock when the person lays on thesupport and prevent the person from sinking into the support. This maynegate the pressure relieving purpose of the support.

In various embodiments, the flexible side walls 80, 82 and to someextent the flexible end walls 88, 90 in combination with the collapsibleinflatable chambers 170, may create a tension relieving hinge shown inFIG. 18. As the inflatable chambers 170 are deflated, the person layingon the underbody support 3 sinks into the underbody support 3, depressedby the weight of the patient 180 on the upper surface. When depressed bythe weight of the patient 180, the upper surface (e.g., upper surface of160, 20, FIG. 18) pulls the materials of the upper surface of theunderbody support 3 toward the center line of the underbody support 3.This would cause hammocking but for the flexible side walls 80, 82hinging inward 190 as shown in FIG. 18, to provide strain relief for thematerials of the upper surface (e.g., 160, 20 in FIG. 18).

Surgeons have been known to complain about legacy air mattresses usedduring surgery. Since the patient is “floating” on a cushion of air,they also tend to move when they are leaned against or pulled, as in thefirm application of a surgical retractor. The lateral movement of theanesthetized patient can make the delicate sewing or cutting of thesurgical procedure more challenging. Therefore, it is advantageous tohave a stabilizing means in conjunction with the air mattress to preventinadvertent lateral movements of the patient on the mattress. In variousembodiments, the flexible side walls 80, 82 and to some extent theflexible end walls 88, 90 in combination with the collapsible inflatablechambers 170, may create a tension relieving hinge as shown in FIG. 18.As the inflatable chambers 170 are deflated, the person laying on theunderbody support 3 mattress sinks into the underbody support 3,depressing by the weight of the patient 180, the upper surface (e.g.,160, 20 in FIG. 18). Depressing the upper surface pulls the materials ofthe upper surface of the support toward the center line. This causes theflexible side walls 80, 82 to hinge inward 190 as shown in FIG. 18. Inthis position, the top of the flexible side walls 80, 82 are moved intoa position proximate the sides of the patient laying on the underbodysupport 3. The flexible side walls 80, 82 are relatively stiff comparedto the inflatable chambers 170 and when the side walls 80, 82 abut thesides of the patient, they stabilize the patient preventing lateralmovement that may be caused by the surgeon leaning or pulling thepatient. By configuring the flexible side walls 80, 82 to hinge inward190 as shown in FIG. 18, they effectively stabilize the patient fromlateral movement.

Indentations 96 may advantageously be added to the inner surface of theflexible side walls 80, 82 that correspond with the rounded ends of theinflatable chambers 170. These indentations 96 in the foam flexible sidewalls 80, 82 create more space for the hinging action of the flexibleside walls 80, 82. The hinging action that may result in strain relieffor the materials of the upper surface can be achieved by creating aspace in the internal region of the underbody support 3 into which theflexible side walls 80, 82 can hinge inward. This space may be createdby the deflating of the volume-controlled, inflatable chambers 170. Asthe inflatable chambers 170 collapse to a smaller volume creating anempty space, the flexible side walls 80, 82 may hinge inwardly into thenewly formed space, providing strain relief for the materials of theupper surface. Since pressure regulated inflatable chambers may not beable to safely collapse to a partial volume, inflatable mattresses withpressure control may not be able to create the hinging action and strainrelief of this invention.

In some embodiments as shown in FIGS. 19 and 20, the underbody support 3may include the assembly of inflatable chambers 170 of the instantinvention, advantageously combined with a heater assembly 1 (FIG. 20),for use when orthopedic surgery positioning apparatuses are used. Forexample, one type of positioning apparatus is a bean bag 520 (FIG. 20)which are large bags full of Styrofoam “beans” that can be put under andthen formed around at least a portion of the patient (e.g., 244). Avacuum removes the air from within the bean bag 520, locking theotherwise flexible, malleable bag full of beans, into a firm shape thatcan be used to hold the patient in a given position such as laying ontheir side (lateral) 244 for hip surgery. The part of the stiffened beanbag 520 under the patient (e.g., 244) is a relatively hard, uneven,lumpy surface that can cause significant localized pressure to beapplied to the patient's skin, causing pressure ulcers. Another exampleis the well-known peg board positioner. In this case a board with holesin it is placed on top of the mattress of the surgical table. Thepatient is positioned on their side (laterally) 244 and held firmly inthis position by pegs (not shown) that are inserted into holes in theboard and pressed firmly against the front and back sides of thepatient. Lying on a hard board obviously increases the chances ofpressure ulcers forming. However, the surgeons need the patients to bewell-secured and stabilized, especially for operations such as hipreplacements that require sawing and hammering. Padding these hard andirregular surfaces while preserving their ability to stabilize thepatient, is very difficult.

In some embodiments, it is advantageous to shorten the inflatablechambers 170 (e.g., transverse inflatable chambers) so that they extendover approximately the middle ⅔ of the table width (e.g., centralportion). This allows the patient who is lying on their side, to besupported by the inflatable chambers but the ends of the chambers do notinterfere with the pegs of the peg board or the vertical side wallsformed by the bean bag. The weight of the patient is supported by theinflatable chambers 170 but the securing function of the positioningapparatuses is not encumbered.

In some embodiments as shown in FIG. 19, the heater assembly 1 (FIG. 20)overlaying the underbody support 3, extends as lateral portions 522beyond the ends of the transverse array of inflatable chambers 170. Theflexible heater assembly 1, can be folded upward along the front andback of the laterally positioned patient (e.g., 244), withoutinterfering with the security of the bean bag 520 or peg board. In thisposition, the lateral portions 522 of the heater assembly 1 are tuckedbetween the patient and the positioning apparatus (e.g., 170, 520),which holds the heater assembly 1 against the patient's skin (e.g., 244)for optimal heat transfer.

In some embodiments, the algorithm for controlling the heated mattressoverlay (e.g., 3, 1, 170, 520) during certain uses, such as orthopedicsurgery, may be different than previously described. For example, it maybe advantageous to have the mattress overlay (e.g., 3, 1, 170) fullydeflated while positioning the patient and forming the bean bag 520 orinserting the pegs in the peg board. As shown in FIG. 20, the flexibleheater assembly 1, is folded up against the patient's front and backside and held in that position by the bean bag 520 or peg board pegs.

Once the patient is positioned, the staff may start the controlalgorithm, which actuates the air pump(s) to inflate the inflatablechambers 170 from their collapsed condition. In the collapsed ordeflated condition, the most if not all of the compression sensitiveswitches 200 will be in the closed position due to the weight of thepatient. Air is pumped into the inflatable chambers 170 until thecompression sensitive switch 200 in the most depressed chamber opens.When this last switch 200 opens, the electric current ceases flowing tothe controller and the control algorithm interprets this as evidencethat the patient is totally supported by air with no pressure points. Nocontact is occurring between the dependent, weight bearing skin of thepatient and the hard surface of the bean bag 520 or peg board.

In some embodiments, the compression sensitive switches 200 in their“open” position (indicating that the patient is well supported) then maybecome safety sensors. If due to movement of the patient or inadvertentair loss from the system, the most protruding part of the patientcontacts the bean bag 520 or peg board, the compression sensitive switch200 at that location closes, causing the control algorithm to add moreair to the inflatable chambers 170 until the compression sensitiveswitch 200 reopens indicating a safe condition. The control algorithmmay also sound an alarm to alert the surgical staff of the patientcontact. The compression sensitive switches 200 may also serve as adocumentation system for safety. If the control algorithm documents thatnone of the compression sensitive switches 200 were closed for aprolonged period of time during any operation, it can be assumed thatthe patient was not subjected to prolonged pressure against the skin.The documented safe condition may be automatically charted in theelectronic medical record (EMR), protecting the surgical staff fromliability should a pressure ulcer develop later.

In some embodiments as in FIG. 21, one or more temperature sensors 250may be arranged or configured to be interposed between the heatedunderbody support 3 and skin of the back or another dependent bodysurface of the patient 232 during a temperature measurement. The heatedunderbody support 3 may warm a peripheral thermal compartment 234 of thepatient 230 that is in contact with the heated surface, creating acondition of near thermal equilibrium (e.g., thermal equilibrium or insubstantially thermal equilibrium) between a core thermal compartment236 and the peripheral thermal compartment 234. In this situation, thetemperature of the skin of the patient that is in contact with theheated underbody support 3 accurately reflects core body temperature.

This may be accomplished by sensing the core temperature using thetechnique described in U.S. Patent Application 2012/0238901,Non-invasive Core Temperature Sensor, filed Mar. 17, 2012, for example.In FIGS. 21 and 22, the heating element 10 of the underbody support 3may heat the skin of the patient's back 232 to a temperature slightlygreater than core (Time A

B) and then the temperature of the heating element 10 (e.g., a set-pointtemperature) may be reduced to a temperature equal or below the coretemperature of the patient. When the heating element 10 temperature isreduced or turned off (Time C), a temperature sensor 250 which may be asingle temperature sensor 250 contacting the body surface of the patient232 that is interfaced with the underbody support 3, may detect thedecrease in skin temperature as the excess heat from the peripheralthermal compartment 234 equilibrates by flowing into the core thermalcompartment 236 (Time C

D). The temperature sensor 250 may be a single temperature sensor 250and the body surface of the patient 232 may be the skin of the back ofthe patient.

The curve of plotted skin temperatures in FIG. 22 shows an early phaseof rapid temperature reduction (Time C

D), followed by a phase of slow or even zero temperature reduction (TimeD

E). The temperature at the point where the temperature curve transitionsfrom rapid reduction to slow reduction (Time D), may correlate with thetemperature at which equilibrium is reached between the peripheral andcore thermal compartments 234, 236 (Time D

E). At equilibrium, the measured peripheral temperature can reliablycorrelate with core temperature. Alternately, the temperature may berecorded at a predetermined time after the heater temperature is reduced(Time E), for example between 1 and 5 minutes, when equilibrium betweenthe peripheral compartment 234 and the core compartment 236 of thepatient can be assumed to have been reached.

In some embodiments, determining when the equilibrium has been reachedbetween the peripheral compartment 234 core compartment 236 may bedetermined by calculations calculated at regular intervals or on anongoing basis rather than at a predetermined time. For example, the rateof temperature change (dT/dt) of the peripheral compartment 234 fallingbelow a rate of temperature change threshold may be used to indicatethat equilibrium has essentially been reached and the temperature may beread. In some embodiments, a comparison of a first rate of change over afirst time period, to a second rate of change over a second time periodfalling below some value (e.g., percent change or the difference betweenthe first rate of change and the second rate of change) may indicatethat equilibrium has essentially been reached.

The temperature sensor 250 may be a thermistor or thermocouple mountedon a thermally insulating material 252, such as a disc of foam. Thethermally insulating material 252 may be many sizes and shapes but mayoptionally be between ½-1 inch in diameter and may be ⅛-⅜ inch thick.The thermally insulating material 252 may thermally insulate thetemperature sensor 250 from direct thermal contact with the heatingelement 10 (e.g., low mass thermal heater). The temperature sensor 250may be placed so that it is directly contacting the body surface of thepatient 232 and is thus positioned between the body surface of thepatient 232 and the underbody support 3. For example, the temperaturesensor 250 may be in contact with the skin of the back of the patient232. Although any other suitable skin surface may be used. The thermallyinsulating material 252 that may be attached to the temperature sensor250 may be interposed between the temperature sensor 250 and the heatingelement 10, minimizing the direct influence of the heating element 10 onthe temperature sensor 250. In some embodiments, the one or moretemperature sensors 250 are not interposed as previously described, butrather is surrounded (e.g., about its diameter), by the heated underbodysupport 3.

When first used, such as at the beginning of a surgical procedure, theperipheral thermal compartment 234 may be much cooler than the corethermal compartment 236 (Time A), and the temperature of the heatingelement 10 may be raised well above the normal safe operatingtemperature for a heated support, for a short time. This heats theperipheral thermal compartment 234 faster (Time A

B), allowing a faster initial temperature recording and more rapid onsetof effective patient warming. For example, if the normal safe operatingtemperature for a heated underbody support 3 is 40° C., the underbodysupport may be initially heated to 45° C. for 5-15 minutes and thenautomatically reduced to the normal safe operating temperature of 40° C.

Another way to approximate core temperature utilizes the fact that theheater assembly 1 of the underbody support 3 cannot be significantlywarmer than the core thermal compartment 236 and not cause thermalinjuries. In this condition, if the temperature sensor 250 is in contactwith the skin of the patient's back 232 and the temperature sensor 250is thermally insulated 252 from direct contact with the heating element10 and/or heater assembly 1, the core thermal compartment 236temperature can be approximated once the peripheral thermal compartment234 has been warmed and allowed to be brought into equilibrium with thecore thermal compartment 236 temperature.

The temperature monitor may include a power supply switch to facilitatethe steps of heating and rapid cooling of the heating element 10, andthus the heater assembly 1. For example the power supply switch cansupply power to the heater assembly 1 to control the heating element 10(e.g., low thermal mass heater) to a temperature that is greater thancore thermal compartment temperature 236. Then the heating element 10temperature rapidly reduces to a temperature that is less than the corebody temperature 236 when the power supply switch cuts off power to theheating element 10. It may be preferable to discontinue power to theheating element 10, however, in some embodiments, the power may besubstantially discontinued rather than completely discontinued. Forexample, the power may be reduced by 90%, or the cycle time betweenpower supplies may be reduced by 90%.

An alternative way which may be used to determine core temperature isfor the temperature monitor to have two temperature sensors (e.g., 250)separated by a small piece of thermal insulation, in a constructionknown as a “heat-flux transducer,” for example. The first temperaturesensor 250 in contact with the body surface of the patient 232 mayreflect the patient's temperature and the second temperature sensor (notshown) in contact with the heating element 10 may reflect the heatingelement 10 temperature. The heating element 10 temperature may thenadjust until the two temperature sensors equal each other and reachequilibrium. At that point there may be zero heat flow (heat flux) andthe patient's core temperature may be equal to the skin temperature.This technique may reduce the heating effectiveness of the surface ofthe heater assembly 1, but it will allow continuous temperaturemonitoring.

Various temperature monitoring techniques described herein use theheating element 10 of the underbody support 3 to equilibrate thetemperature of peripheral thermal compartment 234 with the temperatureof the core thermal compartment 236. These temperature monitoringtechniques may also efficiently use the heating element 10 and underbodysupport 3 itself as the thermal insulation between the patient and theenvironment.

The temperature monitoring techniques of the instant invention may relyon excess heat being added to the peripheral thermal compartment 234.The excess heat may then be allowed to flow into the cooler core thermalcompartment 236 (Time C

D) until thermal equilibrium is reached (Time D

E). This is different than all other core body temperature monitors thatattempt to measure the temperature of the heat flowing out from the corethermal compartment 236 to the peripheral thermal compartment 234 andthen to the skin (e.g., 232).

In some embodiments, the underbody support 3 includes a groundingelectrode for electro-surgical equipment. As shown in FIGS. 2-4, thegrounding can be accomplished by placing an electrode 254 under thepatient but not in direct electrical contact with the patient. Electrode254 may be a large electrode. This can create a condition of capacitivecoupling for grounding the RF electrical current without actuallytouching the patient. These capacitive coupling grounding electrodes 254are well known in the art. For example, U.S. Pat. Nos. 6,053,910 and6,214,000 describe embodiments which may be used. However, thesecapacitive coupling electrodes have been generally utilized as mattressoverlays which are inconvenient and require extra cleaning. Further,these electrodes may be embedded into a gel pad, resulting in an overlaythat is heavy, cumbersome and interferes with optimal pressureoff-loading.

To avoid these problems, various embodiments include capacitive couplinggrounding electrode 254 in the stack construction of the underbodysupport 3. The preferred location for the capacitive coupling electrode254 in the stack is under the compressible material layer 20; however,other locations are anticipated. The electrode 254 may include orconsist of a sheet of flexible and preferably stretchable electricallyconductive fabric that extends substantially across the entire area ofthe underbody support 3. The stretchable fabrics may be woven twills orknits, for example. If a non-stretchable or less stretchable fabric suchas woven nylon or polyester is chosen, care must be taken in the designto avoid anchoring the non-stretchable fabric to the periphery of theunderbody support 3 in order to prevent “hammocking” Various methods ofpreventing hammocking have been discussed in other applications alreadyincorporated herein.

The electrode 254 may be a conductive fabric electrode that may becoated with silicone rubber, as described in U.S. Provisional PatentApplication 61/812,987, to prevent electrical contact with the otherelectrically conducting components while maintaining optimal flexibilityand stretchability. In some embodiments, the conductive fabric groundingelectrode 254 may be the heating element 10 (e.g., conductive fabricheater material, fabric or film). Proper grounding of the heatermaterial (e.g., heating element 10) may provide electrosurgicalcapacitive grounding without the need for an additional layer ofconductive material.

To clean and sanitize medical equipment, hydrogen peroxide (H₂O₂)disinfecting solutions have recently been introduced into the operatingroom and hospital. H₂O₂ is a well-known, powerful oxidizing agent thatkills bacteria and viruses in a mechanical way that cannot lead toresistant strains. The oxidation reaction causes the H₂O₂ to break downinto water and oxygen, two harmless, or less harmless by-products. Theproblem is that H₂O₂ vapor is also highly oxidizing for electricalcomponents, including flexible heater materials (including polypyrrole),metal bus bars and conductive metal coatings such as silver on fabric orthread. There is a need for better protection of the sensitiveelectrical components from oxidation by H₂O₂ and other oxidizers.

In some embodiments, urethane film may be used as the shell 42, 44material for the underbody support 3 or related blankets, because of itsstrength, flexibility durability and response to heat sealing.Unfortunately, although urethane film may be good for providing awater-resistant and encapsulating shell 42, 44, urethane film isrelatively permeable to hydrogen peroxide vapors, allowing the highlyoxidizing vapors to enter the underbody support 3 or a related heatedelectric blanket. Once inside, the peroxide vapors attack any oxidizablematerial. These vapors can cause oxidation and failure of electricalcomponents, especially polypyrrole. Other plastic films such as PVC aremuch less permeable to peroxide vapor than urethane. Since peroxide isbecoming more and more common as a disinfectant for operating room andother hospital use, a way of protecting vulnerable internal componentsfrom oxidation due to peroxide is needed.

In some embodiments, the underbody support 3 or the related heatedelectric blankets incorporate certain materials that can protect thepolypyrrole heater (e.g., heating element 10) and other oxidizableelectrical components from oxidizing agents such as hydrogen peroxide(H₂O₂) disinfecting solutions. In some embodiments, a catalyst toaccelerate hydrogen peroxide decomposition may be coated on orimpregnated into an element within the shell 42, 44, or on the interiorsurface of the shell 42, 44.

In some embodiments, sacrificial materials may be included in theinternal construction that can be preferentially oxidized. Sacrificialmaterials may be organic materials such as cellulose. For example,sacrificial materials such as one or more sacrificial layers 256 ofcotton, linen or paper, as shown in FIGS. 2-4, may be added to theinside of the underbody support 3 or the related heated electric blanketso that the peroxide vapors preferentially attack and oxidize thesacrificial material. Other oxidizable sacrificial materials may beused. In the process of oxidizing these sacrificial materials, theperoxide breaks down into inert (e.g., less corrosive, less problematic)water and oxygen before it can attack the electrical components. Thecatalyst for accelerating hydrogen peroxide decomposition may decomposeall, substantially all, or the majority of the hydrogen peroxide vaporsbefore they reach the electrical components, depending on how thecatalyst is incorporated into the particular apparatus.

In some embodiments, materials that are known to be catalysts for thebreakdown reaction of peroxide to water and oxygen may be added. Forexample, manganese dioxide (MnO₂) powder may be added to one or more ofthe sacrificial layers 256 in FIGS. 2-4, or the compressible materiallayer 20, the inside surface of the shell 42, 44, or adhered directly toany suitable component of the heater assembly 3 by an applied coating,by impregnation into, by adhesive, or by any other suitable process.

In some embodiments, the insoluble manganese dioxide powder may besuspended in water and the sacrificial layer 256 of fabric or foam canbe dipped in this water/manganese dioxide powder suspension to evenlydisperse the powder throughout the sacrificial layer 256 of fabric orfoam when the water evaporates. In some embodiments, a small amount ofmethyl cellulose can be added to the water/manganese dioxide powdersuspension in order to increase the duration of the suspension time ofthe powder in water. The small amount, or sufficient amount of methylcellulose to increase the viscosity of the water and manganese dioxidesuspension to between 10 and 120 centipoise. The methyl cellulose mayalso act as a binding agent, improving adherence of the manganesedioxide powder to the fabric, foam or other material. Other bindingagents, and/or suspension improvers besides methyl cellulose may beused. Adding too much binding agent (e.g., greater than 120 centipoise)can cause the binding agent to completely encapsulate the manganesedioxide powder when it dries, and too little (e.g., less than 10centipoise) will not hold the powder in suspension very long. Othercarriers besides water may also be used.

In some embodiments, the one or more sacrificial layers 256 of manganesedioxide impregnated fabric or compressible material layer 20 may beadded to the inside of the underbody support 3 or related heatedelectric blanket so that the catalyst can preferentially attack theperoxide vapors and neutralize them to water and oxygen, before they candamage the electrical components. Other liquids are anticipated forsuspending the manganese dioxide powder. Examples of catalysts that canbe used in place of manganese dioxide powder include: silver, platinumand transition metal salts. Other catalysts may also be used. In someembodiments the catalysts may be added to another feature of theunderbody support 3 or the related heated electric blanket, and to amaterial other than fabric or foam.

The effectiveness of these measures for preventing the oxidation anddegradation of the heater fabric and other mattress or blanketcomponents by peroxide vapor were tested. During testing similar squaresof heater material with bus bars attached were sealed into shells ofurethane film. The heaters were then placed into a chamber thatcontinuously exposes the shell to peroxide vapor. Over the course of9-12 days, the change in resistance of the heater material was measuredand correlated with the degradation of the conductance of the heatermaterial. Over the course of 9 days of exposure to peroxide vapor, theresistance of unprotected polypyrrole heater material increased from58.4 to 238.2 ohms on the square. The significant increase inresistance, indicates that the conductivity of the unprotectedconductive heater material (e.g., heating element 10) was rapidlydegraded by the peroxide vapors.

Over the course of 12 days of exposure to peroxide vapor, the resistanceof heaters that included two layers of sacrificial cotton fabric insidethe shell, increased from 53.5 to 84.8 ohms on the square. Over thecourse of 12 days of exposure to peroxide vapor, the resistance ofheaters that included two layers of polyester fabric impregnated withmanganese dioxide inside the shell, did not increase resistance at all(52.8 to 52.8 ohms on the square). The MnO₂ was very effective as acatalyst neutralizing the peroxide vapor before it could destroy theheater. The sacrificial layer of cotton fabric was also quite effectivein protecting the heater but less so than the MnO₂.

This disclosure of using MnO₂ or sacrificial cellulose layers to protectoxidizable components, especially electrical components, is not limitedto underbody supports 3 and heating blankets. In some embodiments, othermedical equipment (e.g., apparatus) including electrical components suchas patient monitors, patient monitoring electrodes, patient monitoringsensors and medical equipment control circuits may be protected fromoxidation and damage by peroxide vapors or liquid, by incorporating MnO₂or sacrificial cellulose layers into the equipment, as disclosed in thisapplication.

In some embodiments, the underbody support 3 uses the fact that thepatient sinks into the underbody support 3 and achieves maximal bodysurface contact with the underbody support 3, to aid in preventing thepatient from sliding off of the surgical table 412 when placed in thesteep Trendelenburg position (head down). This is in contrast to atraditional mattress wherein the torso of the patient may only contactthe mattress at the buttocks and shoulders. This relatively smallcontact area means that the coefficient of friction must be much greaterin order to prevent the patient from slipping off of the mattress whenplaced in the Trendelenburg position. Various embodiments allow contactwith the entire back of the patient and curve up along their sidesallowing a much lower coefficient of friction to prevent slipping.

The underbody support 3 may include elements for anchoring the supportto the surgical table 412. In some embodiments, the elements foranchoring may be a Velcro attachment between the upper surface of thesurgical table 412 and the lower surface of the underbody support 3. Insome embodiments, the elements for anchoring may be a strap attachmentbetween the side of the surgical table 412 and the underbody support 3.The lower surface may also be called the table interface surface.

In some embodiments, a sheet of fabric that has been at least partiallycoated on both sides with high-friction plastic or rubber, or a materialhaving similar characteristics, may be interposed between the patientand the support in order to increase the coefficient of friction. Anexample of this may be PVC or silicone that may be applied as a threedimensional pattern or three dimensional raised dots, onto a fabric(e.g., friction enhancing elements). The high-friction plastic or rubberthat may be in the form of a pattern or dots, “grip” the upper surfaceof the underbody support 3 on one side and the back of the patient ontheir other side, dramatically increasing the coefficient of frictionbetween the patient and the underbody support 3 surface, preventing thetwo from slipping against each other. Alternately, the high-frictionplastic or rubber forming a pattern or dots may be applied directly tothe upper surface of the underbody support 3. The upper surface may alsobe called a patient interface surface.

In some embodiments, a method of supporting and restricting a slidingmotion of a patient on a surgical table including the features describedpreviously herein includes (i) providing an underbody support configuredto support the patient on the table, the underbody support including acompressible material layer having an upper surface configured to facethe patient opposite a base layer having a lower surface configured toface the surgical table; (ii) coupling the underbody support to thesurgical table; (iii) placing a layer of material between the uppersurface of the underbody support and the patient, the layer of materialcomprising friction enhancing elements on both sides of the layer ofmaterial, wherein the layer of material is configured to grip both theunderbody support and the patient to prevent the patient frominadvertently slipping off the underbody support; and (iv) positioningthe patient on the underbody support.

In some embodiments of the method, the layer of material may be a drawsheet that is configured to be positioned over the underbody support forlifting the patient. In some embodiments the layer of material includingfriction enhancing elements includes PVC or silicone.

In some embodiments of the method, positioning the patient on theunderbody support comprises positioning the patient in the head downTrendelenburg position, the friction enhancing elements being configuredto reduce sliding of the patient relative to the underbody support whenthe patient is positioned on the underbody support in the head downTrendelenburg position.

In some embodiments of the method, the underbody support includes twoside walls; two end walls; a base layer having a lower surfaceconfigured to face the table and a base layer perimeter; thecompressible material layer may have a compressible material layerperimeter, the compressible material layer bonded to the two side wallsand to the two end walls about the perimeter of the compressiblematerial layer; and one or more inflatable chambers, wherein the twoside walls and two end walls are fastened to the perimeter of the baselayer, and the base layer, the two side walls, the two end walls, andthe compressible material layer form a box-like structure made offlexible foam. In some embodiments the box-like structure surrounds theone or more inflatable chambers.

In some embodiments of the method, the upper edges of the two flexibleside walls can hinge inward in response to the weight of a patientdepressing the central region of the layer of compressible material, andthe hinging inward of the flexible side walls allows the layer ofcompressible material to deform maximally while accommodating thepatient without creating a hammock effect.

In some embodiments of the method, the upper edges of the two flexibleside walls can hinge inward in response to the weight of a patientdepressing the central region of the layer of compressible material, andthe hinging inward of the flexible side walls allows the tops of theflexible side walls to substantially abut the sides of the patientstabilizing the patient against inadvertent lateral movement.

In some embodiments of the method, the method may further include:placing the patient in the head down Trendelenburg position, andfastening shoulder straps that extend from a head end portion of theunderbody support over the shoulders of the patient to a central portionof the underbody support or the surgical table when the patient is inthe head down Trendelenburg position to secure the patient to thesurgical table.

In some embodiments as shown in FIGS. 23 and 24, a cushion 400 (e.g.,foam cushion) may be anchored to the head end of the support surface 410and extend onto the mattress portion at the head end of the surgicaltable 412. The cushion 400 may optionally be substantially yoke-shapedextending transversely across the surgical table 412, with a depressionin the middle to accommodate a patient's head 240 and neck 242 and withraised lateral portions 402 to engage the patient's shoulders 238. Theraised lateral portions 402 interface with a patient's shoulders 238, toeffectively prevent the patient from slipping off of the head end of thesurgical table 412. Other cushion shapes may also be used. The cushion400 may be formed of foam or any other suitable material.

In some embodiments, the yoke-shaped cushion 400 may also includeshoulder straps 404, much like the shoulder straps of a backpack, mayextend substantially from a yoke-shaped cushion 400 over the front ofthe patient's shoulders 238 and anchor on side rails 414 of the surgicaltable 412 or other surface. For example, at a central portion of theunderbody support 3. Other strap configurations may be used foranchoring the yoke-shaped cushion 400 to the side rails 414 of thesurgical table 412. The anchoring shoulder straps 404 may be adjusted inlength as well as anchored at different locations along the side of thesurgical table 412, or another part of the surgical table 412 allowingthe patient to be repositioned along the surgical table 412 ifnecessary. In some embodiments, the yoke-shaped cushion 400 may beattached to and anchored to the head end of the underbody support 410.In some embodiments, the yoke-shaped cushion 400 may also include one ormore cushion inflatable chambers to minimize point pressure on thepatient's shoulders 238. The cushion inflatable chambers of theyoke-shaped cushion 400 may be similar or different to inflatablechambers 170 previously disclosed.

In some embodiments as shown in FIGS. 25-27, the underbody support 3includes a layer of water-circulating channels 500 that optionally coversubstantially the entire surface area of the underbody support 3. Thelayer of water-circulating channels 500 may be located near the patientsurface of the underbody support 3, or the yoke-shaped cushion 400,including the raised lateral portions 402. Cold water may optionally becirculated through water-circulating channels 502 for inducingtherapeutic hypothermia. Hypothermia has been shown to beneuro-protective for: closed head injuries; post successful CPR forheart attacks and for some strokes. Therapeutic cooling has is alsouseful for heat stroke and certain hypermetabolic states like malignanthyperthermia.

The water-circulating channels 502 may be molded into the two filmlayers 510, 512 of polymeric film that are then sealed together 504(e.g., hermetically sealed) between the water-circulating channels 502.This construction of a layer of water-circulating channels 502 may bedone according to methods known in the art. Relatively thick PVC orurethane film may be used for this purpose. The sealed portions 504 maybe created using RF, ultrasound, heat, or any other suitable method ofsealing. This construction results in a flexible layer ofwater-circulating channels 500 that can be positioned near the uppersurface of the underbody support 3. Since the film layers 510, 512forming the water-circulating channels 502 are relatively thick, theymay also be relatively resistant to collapse from supporting the weightof a patient.

In some embodiments, longitudinal slits are made through the sealedportions 504 of the layer of water-circulating channels 500. Theselongitudinal slits allow lateral expansion of the layer ofwater-circulating channels as the layer is deformed by the weight of apatient. The lateral expansion of the layer of water-circulatingchannels 500 due to the slits may facilitate the accommodation of thepatient into the underbody support 3, while preventing “hammocking.”

An advantage of adding a layer of water-circulating channels 500 to theinflatable underbody support 3 of various embodiments is that thepatient sinks further into this underbody support 3 than into a foammattress, for example. By sinking into the underbody support 3, theunderbody support 3 may curve up along side the patient forcing thewater-circulating channels 500 into close opposition to the patient'sskin over a much larger surface area than can be accomplished with afoam mattress. The greater surface area in contact with the coldwater-circulating channels 500 results in more effective heat or coldtransfer. Therefore, the combination of the maximally accommodatingunderbody support 3 of various embodiments with a layer ofwater-circulating channels 500 is both unique and advantageous.

In some embodiments as shown in FIG. 26, the upper surface of the layerof water-circulating channels 500 may have a coating of gel 514 to fillin the uneven surface created by the molded channels. The gel coatingproduces a relatively smooth upper surface for contacting the patientwhile maintaining thermal conductivity. Alternately, in some embodimentsas shown in FIG. 27, the molded channels are only molded into the lowerfilm layer 512 of polymeric film. This leaves the upper film layer 510of polymeric film smooth for optimal contact with the patient.

Whereas particular embodiments of the invention have been described forthe purposes of illustration, it will be evident to those skilled in theart that numerous variations of the details may be made withoutdeparting from the invention as set forth in the embodiments describedherein.

1. A non-invasive core temperature monitor for monitoring thetemperature of a patient, the core temperature monitor comprising: aheated underbody support for heating and supporting at least a portionof the patient, the heated underbody support including a low thermalmass heater that is configured to be in thermal contact with at least aportion of the patient during a core temperature measurement; atemperature sensor configured to be interposed between an upper surfaceof the low thermal mass heater and the patient during temperaturemonitoring, the temperature sensor further configured to be in thermalcontact with the patient's skin during temperature monitoring; a switchthat controls electric power to the low thermal mass heater; whereinactivation of the switch can rapidly reduce the electric power suppliedto the low thermal mass heater allowing the low thermal mass heater torapidly cool.
 2. The non-invasive core temperature monitor of claim 1,wherein the low thermal mass heater is made of electrically conductivefabric, film or foil.
 3. The non-invasive core temperature monitor ofclaim 1, wherein a small amount of thermal insulating material isinterposed between the temperature sensor and the low thermal massheater.
 4. The non-invasive core temperature monitor of claim 1, whereinthe temperature of the low thermal mass heater is controlled to atemperature that is greater than the core temperature of the patient,and then rapidly reduced to a temperature that is less than the coretemperature of the patient when the switch is activated.
 5. Thenon-invasive core temperature monitor of claim 4, wherein the activationof the switch also activates a timer that measures a predeterminedamount of time to pass while the over-heated peripheral thermalcompartment of the patient cools and comes into thermal equilibrium withthe core thermal compartment at a predetermined thermal equilibriumtime; when the predetermined thermal equilibrium time is reached, thetemperature sensor measures the skin temperature of the patient; whereinthe skin temperature reflects the temperature of the peripheral thermalcompartment that is in thermal equilibrium with the temperature of thecore thermal compartment and thus the measured skin temperaturecorrelates with the core temperature of the patient.
 6. The non-invasivecore temperature monitor of claim 5, wherein the predetermined amount oftime is in the range of 0.5-5 minutes.
 7. The non-invasive coretemperature monitor of claim 4, wherein the activation of the switchactivates an algorithm that monitors the temperature-time curve of themeasured skin temperatures following the rapid reduction in heatertemperature.
 8. The non-invasive core temperature monitor of claim 7,wherein core temperature corresponds to the temperature of thetemperature-time curve at which a rapid decline in measured skintemperature transitions to a gradual decline in the measured skintemperature.
 9. The non-invasive core temperature monitor of claim 5,wherein the measured skin temperature is compared to a desired patienttemperature and the result of this comparison is used to automaticallycontrol a set-point operating temperature of the heated underbodysupport.
 10. The non-invasive core temperature monitor of claim 8,wherein the measured skin temperature is compared to a desired patienttemperature and the result of this comparison is used to automaticallycontrol the set-point operating temperature of the heated underbodysupport.
 11. A method for non-invasive core temperature monitoring, themethod comprising: providing a heated underbody support for heating atleast a portion of a patient, the heated underbody support comprising: alow thermal mass heater arranged to be in thermal contact with at leasta portion of the patient during core temperature monitoring; atemperature sensor configured to be in thermal contact with thepatient's skin to measure the temperature of the peripheral thermalcompartment of the patient during temperature monitoring; a switch thatcan rapidly reduce the electric power supplied to the low thermal massheater; controlling the low thermal mass heater to a temperature that isgreater than the core temperature of the patient; activating the switchto rapidly reduce the temperature of the low thermal mass heater to aset-point temperature that is less than the core temperature of thepatient; and measuring the temperature of the peripheral thermalcompartment that is in substantially thermal equilibrium with thetemperature of the core thermal compartment.
 12. The method of claim 10,wherein activating the switch activates a timer, and wherein measuringthe temperature of the peripheral thermal compartment that is in thermalequilibrium with the temperature of the core thermal compartmentcomprises waiting a predetermined amount of time after activating theswitch to allow the over-heated peripheral thermal compartment of thepatient to cool and come into thermal equilibrium with the core thermalcompartment.
 13. The method of claim 11, wherein the predeterminedamount of time is in the range of 0.5-5 minutes.
 14. The method of claim11, wherein the low thermal mass heater is made of electricallyconductive fabric, film or foil.
 15. The method of claim 11, whereinactivating the switch activates an algorithm that monitors thetemperature-time curve of the peripheral thermal compartment followingthe rapid reduction in heater temperature, and wherein measuring thetemperature of the core thermal compartment comprises monitoring thetemperature-time curve to determine when a rapid decline in measuredskin temperature transitions to a gradual decline in measured skintemperature indicating that thermal equilibrium between the peripheralthermal compartment and the core thermal compartment has been reachedand the temperature of the peripheral thermal compartment issubstantially equal to the temperature of the core thermal compartment.16. The method of claim 15, wherein the low thermal mass heater is madeof electrically conductive fabric, film or foil.
 17. The method of claim15, wherein thermal insulating material is interposed between thetemperature sensor and the low thermal mass heater.
 18. A non-invasivecore temperature monitor for monitoring the temperature of a patient,the core temperature monitor comprising: a heated underbody support forheating at least a portion of a patient; the heated underbody supportincluding a low thermal mass heater, the low thermal mass heaterconfigured to be in thermal contact with at least a portion of thepatient during temperature monitoring, the low thermal mass heaterconfigured to heat the peripheral thermal compartment of the patient toa temperature that is greater than the core temperature of the patient;a temperature sensor configured to be in thermal contact with thepatient's skin during temperature monitoring; a switch, or an algorithmof a processor, that is configured to reduce the temperature of the lowthermal mass heater to a set-point temperature that is less than thecore temperature of the patient allowing the temperature of the lowthermal mass heater to move towards being in thermal equilibrium withthe core body temperature of the patient, and wherein the algorithmmonitors the temperature-time curve; and wherein the core temperature ofthe patient corresponds to the temperature sensed by the temperaturesensor when the peripheral thermal compartment of the patient is insubstantial thermal equilibrium with the temperature of the core thermalcompartment of the patient.
 19. The core temperature monitor of claim18, wherein the low thermal mass heater is made of electricallyconductive fabric, film or foil.
 20. The support of claim 18, whereinthe switch, or the algorithm of the processor, is configured todiscontinue or substantially reduce the power that is supplied to theheater assembly.
 21. The support of claim 18, wherein the temperature ofthe peripheral thermal compartment that is in substantial thermalequilibrium with the temperature of the core thermal compartment isdetermined by waiting a predetermined amount of time.
 22. The support ofclaim 18, wherein the temperature of the peripheral thermal compartmentthat is in substantial thermal equilibrium with the temperature of thecore thermal compartment is determined by monitoring thetemperature-time curve to determine when a rapid decline in measuredskin temperature transitions to a gradual decline in measured skintemperature indicating that thermal equilibrium between the peripheralthermal compartment and the core thermal compartment has been reachedand the temperature of the peripheral thermal compartment issubstantially equal to the temperature of the core thermal compartment.